1. Field of the Invention
The invention relates to the field of wind turbine power generation, and in particular to a wind turbine that can be utilized on a utility grid, that is able to provide a wide range of frequency and voltage output, that can be used as a stand-alone power source, and that includes manufacturing and distribution cost and noise reduction features that increase the range of applications.
2. Background of the Related Art
Small-scale wind turbines are in wide and growing use. Small-scale wind turbines are typically used to charge battery banks or to feed power into utility lines. Present wind turbines, however, typically have several weaknesses. They often lack versatility and durability, perform below needed performance levels, fail to provide sufficient cost-effectiveness, and generate unacceptable levels of audible noise. If these benefits were realized, the result would be a turbine that is more attractive for residential and other uses.
For example, one weakness with prior art turbines is their limited ability to perform multiple functions or to be used for a wide range of applications. One turbine design can be used for grid-connected operation. Another design can charge a battery bank for backup to the grid. A third design could be used without the grid as the solitary powering device. However, a different method of connection for each wind generator is required for these uses. Also, depending on the specific application (e.g., to provide a battery bank for stand-alone use), the turbine design often needs to be modified for site-specific conditions (e.g., to provide power at a selected voltage). As a result, prior art wind turbines, which are typically not capable of use in a wide variety of settings, require the manufacturer to stock and distribute a wide variety of wind turbine designs, thereby also complicating manufacturing and inventory logistics.
Another weakness of prior art turbines is the cost and sub-optimal performance of the alternator typically used. Prior art alternators typically contain slots of steel that hold a number of copper windings, which, in connection with the use of permanent magnets, convert the energy of the wind to electrical output. In the prior art design, the slots have often tended to vibrate when in operation. The vibration produces an unacceptable noise and a cogging torque that prevents the wind turbine from starting up or interferes with startup in lower winds. Additionally, prior art alternators typically have low stall torque and high manufacturing costs. A new alternator design is needed that eliminates unnecessary vibrations, increases the stall torque, and decreases manufacturing costs.
Capacitors incur another cost and reliability problem for the single-phase inverters typically used with prior art generators. The main capacitors in prior art turbines are required for storing energy for the oscillating 50 or 60 Hz power level typically produced. However, capacitors add a costly element to the turbine, one that may need replacement or repair over the life of the generator. A system is needed that can use, for example, the kinetic energy of the rotating blades to store energy. Such a kinetic system would increase the life and decrease the cost of the wind turbine system.
In addition, prior art rotor blades in down-wind turbines often generate undesired audible noise during blade rotation. For example, a thump may sound as each blade enters the plane downwind from the turbine's tower, where it experiences a momentary decrease in wind speed. When the rotor turns quickly, many audible thumps are generated, producing undesirable noise. An improved blade design is needed to reduce the sound of the thump, especially for residential areas.